The objective of the proposed research is to measure local rheological properties of the vascular interface and the underlying tissue and correlate these measurements with the histological structure of the underlying tissue in control animals and in animals with experimental atherosclerosis. The motivation for this study comes from the findings of recent researches which point to the possibility that the susceptibility of the various locations of the vascular surface to the atherosclerotic damage is strongly correlated with exposure to hydrodynamic shear stress and also to the local rheological properties of the arterial tissue. Among the specific properties being studied are the shear strength of the endothelial layer and the indentation resistance of the vascular intima and its supporting structures. The former involves the use of fine saline jets to erode the endothelium and the latter is carried out using a microindentor developed by modification of an analytical balance to apply small loads, the resulting indentation being measured by a linear transformer. BIBLIOGRAPHIC REFERENCES: "Strength of the Endothelial Surface of the Canine Aorta," by D.J. Patel, R.N. Vaishnav, H. Bulent Atabek, F. Plowman, J. Kamal and T. Talbot, Proceedings of the Meeting of the Federation of American Societies for Experimental Biology, Vol. 35, No. 3, March 1976. "Some Recent Studies on the Mechanical Properties of the Intimal Layer and Adjacent Flow Fields," by D.J. Patel, R.N. Vaishnav and H. Bulent Atabek, Proceedings of the ASCE - EMD 1976 Specialty Conference, Biomechanics Symposium, May 26-28, 1976, at Waterloo, Canada.